Frog die-off alarms University researchers

Researchers at Washington University have noticed an unusual decline in the number of frog species found in Central America.

Apparently the result of a fungal infection, many frog species are dying off rapidly, leading researchers to worry about the diversity of frog populations and the implications for the region as well as the world as a whole.

Jonathan Chase, director of the Tyson Research Center and co-author of the paper, said there are many mechanisms that can lead to such a decline.

“Usually the first culprit is habitat loss—when you lose area you lose species,” Chase said. “It’s the most important relationship in ecology.”

Chase also discussed the role of the fungus in the frogs’ decline. According to Chase, it is suspected that the fungus, amphibian chytrid fungus, is not native to the areas where it is causing extinction and that humans have caused it to travel into the areas. Since the fungus is not native, the frogs have no evolutionary experience with it.

“Oftentimes massive die-offs like this are associated with invasive species,” Chase said.

Kevin Smith, associate director of the Tyson Research Center and first author of the study, has been leading studies looking at the presence of the fungus in eastern central Missouri at Tyson and other natural areas near the St. Louis area.

The fungus is found all over the world but has caused large-scale extinctions in Europe, Australia, Central America and western North America. Chase said there are multiple theories of where the fungus originated, including South Africa and Japan.

“We know the very same pathogen or at least what appears to be the very same pathogen, this amphibian chytrid fungus. It’s causing declines and extinctions in south Central America, in Australia, in Europe and even in other parts of North America, yet in a lot of the eastern United States including Missouri, it seems to be present but doesn’t have any effect at all,” Smith said. “We very rarely find that frogs in this part of the country are associated with this pathogen.”

The rapid extinctions cause fewer and fewer species to make up the bulk of the frog population.

“Biodiversity loss has many implications, some of which are aesthetic—it’s simply sad that we’re losing huge proportions of the species that used to be present, and the loss seems to be something that humans have caused,” Chase said.

Central America was chosen, according to Smith, because it was the first known area to show such extinctions due to the pathogens. He said tracking the pathogen is difficult because it has been known only for 10 years but probably had an effect long before it was discovered. Also, the fungus is microscopic, and other than a few minor symptoms, it is hard to identify infected animals in the field.

“Do frogs affect our daily life? Probably not. But is the extinction of many frogs going to influence the world’s ecosystems? Yeah, [frogs] are a very important species,” Chase said.

Chase cited the fact that frogs feed on many species of insects and play a vital role in the food web and the regional ecology where they are found.

“It doesn’t seem to be causing the massive die-offs that you see in some of these other areas, and that’s another area we’re interested in—trying to understand why,” Chase said.

Chase said studying amphibian populations can give insight into what impact climate change can have for other organisms.

“A lot of people want to say amphibians are canaries in the coal mine,” Chase said. “They tend to be more sensitive to environmental change.”

Changes in regional ecology such as this as well as decline of coral reefs can be indicators of changes happening in the world. Chase said the frog extinctions might be a combination of the fungus, elevated pollution and other factors.

“It shows that if extinctions occur non-randomly, if they’re selective, if there’s a pattern to the way the extinctions are happening, you can end up losing a lot more biodiversity than if it were just random extinction going on,” Smith said.

At the Tyson Research Center, there is ongoing work examining Missouri’s own ecology.

Karen Lips from Southern Illinois University was also an author of the study and collected much of the data. The article ran in the October issue of Ecology Letters.

Smith said the next steps for the studies would be to look at other waves of extinction to see if they are selective and identify the causes. He said it is important to study the pathogen where it does not cause extinctions because one hypothesis is there may be an additional environmental trigger.

“I think it shows how important it is that there are biologists out there doing this kind of work all over the world, because at some point this data is going to be used and this is one of those cases,” Smith said.